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Fetal ultrasound: What can it tell you?
Fetal ultrasound gives you an exciting early glimpse of your baby — but it can tell your health care provider much more. Here's why you might need an ultrasound and what to expect during the exam.
By Mayo Clinic staffMonths before delivery, a fetal ultrasound may give you the chance to study your baby's profile and watch his or her tiny beating heart in action. But this first glimpse of your developing baby isn't done primarily to provide parental thrills or souvenir snapshots. A fetal ultrasound helps your health care provider evaluate your baby's growth and development and determine how your pregnancy is progressing.
Why are fetal ultrasounds done?
For most healthy women with normal pregnancies, routine ultrasounds don't affect the outcome of the pregnancy. So why are they done so often?
Your health care provider may use a fetal ultrasound to:
- Confirm the pregnancy and its location. Some embryos develop in the fallopian tube instead of in the uterus. An ultrasound exam can help your health care provider detect and treat a tubal (ectopic) pregnancy before it endangers your health.
- Determine your baby's gestational age. Knowing the baby's age can help your health care provider more accurately determine your due date and track various milestones throughout your pregnancy.
- Confirm the number of babies. If your health care provider suspects a multiple pregnancy, an ultrasound may be done to resolve the question.
- Evaluate your baby's growth. Your health care provider can use ultrasound to determine whether your baby is growing at a normal rate. Ultrasound can be used to monitor your baby's movement, breathing and heart rate as well.
- Study the placenta. The placenta provides your baby with vital nutrients and oxygen-rich blood. Any problems with the placenta need special attention.
- Identify possible fetal abnormalities. An ultrasound can help your health care provider detect many congenital abnormalities. An early diagnosis may lead to early interventions that help save or improve a baby's life.
- Screen for Down syndrome. Together with certain blood tests, ultrasound can be used between the 11th and 14th week of pregnancy as an initial screening test for Down syndrome, a genetic disorder that causes mental retardation and other problems. Using ultrasound, your health care provider measures a specific region on the back of your baby's neck (nuchal translucency screening test). This first-trimester screening has proved to be at least as accurate as the traditional blood test screening in the second trimester. If the results of the ultrasound and the blood tests suggest a high risk of Down syndrome, further testing can be used to confirm the results.
- Investigate bleeding and other worrisome signs or symptoms. If you're bleeding or having other complications, an ultrasound may help your health care provider determine the cause.
- Perform other prenatal tests. Your health care provider may use ultrasound to guide needle placement during certain prenatal tests, such as checking a sample of amniotic fluid for specific genetic problems (amniocentesis) or testing a sample of the placenta for genetic abnormalities (chorionic villus sampling).
Ultrasounds aren't recommended simply to determine a baby's sex — but it may be a bonus for curious parents when an ultrasound is done for medical reasons.
Can I seek an ultrasound on my own?
If your health care provider doesn't suggest a fetal ultrasound but you'd like the reassurance the test can provide, share your wishes with your health care provider. Work together to determine what's best for you and your baby.
How does ultrasound work?
During a fetal ultrasound, high-frequency sound waves are directed at the tissues in your abdominal area. These sound waves bounce off the curves and variations in your body, including your baby. The sound waves are translated into a pattern of light and dark areas — creating images of your baby on a monitor that can be recorded on film.
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